Concrete and cement are quite often spoken about as if they are the same thing, yet the two are separate construction materials. However concrete can not be made without cement and this is the main difference between the two. Cement is essentially the binder, a fine powder that when mixed with water helps combine the composite materials that are used to make concrete.
What is Concrete?
Concrete consists of aggregate, such as sand or crushed stone, which is mixed with cement and water. The cement and water forms a paste that coats and binds the aggregate, with the water causing a chemical reaction, called hydration, that creates the hardening that sets the concrete. When set, concrete produces a strong and durable construction material that can be used in a diverse range of projects from driveways and home building, to giant dams and skyscrapers.
The key is in the mixing of the component parts, and the ratio of aggregate to water and cement. If there is too little water used, the concrete mix can become hard to work with, while if too much water is used the outcome can be that the final product is weakened. That said, the amount of aggregate used is also very relevant, since it constitutes between 60% to 80% of the concrete. On the whole, good aggregate will contain stone of varied sizes, though with a specific average and maximum size.
Concrete can either be poured directly into the required location, to create foundations or flooring for a new build, or the concrete mix can be shaped in to building blocks or slabs, using molds to suit a project’s requirement. The mix will be poured into the mold before the chemical reaction occurs in order for the mix to harden in to the required shape.
What is Cement?
Cement is a fine powder-like substance, made from natural materials that include limestone, shale and clay, to name a few. The component parts are heated in a kiln to create the small lumps known as ‘clinker’, which in turn are then ground down, while gypsum is added, to form the more familiar cement powder. It becomes a binding agent when this powder is mixed with water.
The most commonly used cement is Portland cement, deriving its name from its similarity as a finished product to Portland stone. It was an English bricklayer called Joseph Aspdin who first made Portland cement, using his own kitchen stove to heat limestone and clay. He was to get a patent for his discovery in 1822, but from such humble beginnings a vast industry was to form.
Portland cement is a hydraulic cement, so when water is added a chemical reaction begins and the cement starts to harden and set. Due to the nature of the compounds created in these chemical reactions, they are insoluble in water, allowing them to retain their strength and durability even underwater.
Concrete and cement therefore are two separate materials used in the construction industry, although cement is a vital ingredient in making concrete. Cement will comprise around 10% to 15% of a concrete mix, before water binds it to the aggregate that constitutes the bulk of the concrete mix. The resulting hardening process carries on for years, and so the concrete can strengthen over time. Portland cement is the most common cement used in the process.